1. Field of the Invention
The present invention relates to a lens barrel provided at the front end thereof with a lens barrier mechanism which is driven to open and close its barrier blades for protecting the frontmost lens surface from being stained or damaged.
2. Description of the Related Art
As an example of a conventional lens barrel having a lens barrier mechanism, a lens barrel which is provided therein with a stationary ring, a rotating cam ring positioned inside the stationary ring, and an exterior ring member positioned between the stationary ring and the cam ring, is known in the art. The cam ring is provided with a set of follower pins, and the exterior ring member is provided with a corresponding set of cam grooves in which the set of follower pins of the cam ring are respectively engaged. The lens barrier mechanism having barrier blades driven to open and close a photographing aperture of the lens barrel is fixed to the front end opening of the exterior ring member. Driving the cam ring to rotate in forward and reverse directions causes the exterior ring member to advance and retreat in an optical axis direction while opening and closing the barrier blades of the lens barrier mechanism, respectively.
In such a conventional lens barrel, the diameter of the exterior ring member is preferably as small as possible from a design point of view. On the other hand, in order for the barrier blades to be widely opened to open the photographing aperture widely, the diameter of the lens barrier mechanism needs to be large. However, the inner diameter of the exterior ring member has to be large if the diameter of the lens barrier mechanism is large.
In the case where one or more cam grooves are formed on an inner peripheral surface of the exterior ring member, the wall of the exterior ring member has to be thick because the cam groove generally has a deep radial depth. Accordingly, the inner diameter of the exterior ring member decreases and increases if the outer diameter of the exterior ring member is decreased and increased, respectively.
Although the diameter of the lens barrel is desirably small from a design point of view, with regard to the outward appearance thereof, each barrier blade of the lens barrier mechanism needs to have a long length if it is desired to provide a large photographing aperture which is opened and closed by the lens barrier mechanism. However, the diameter of the lens barrel increases if the length of the barrier blade is increased.